With the recent advances in small-incision cataract surgery, increased emphasis has been placed on developing soft, foldable materials suitable for use in artificial intraocular lenses (“IOL”). Materials that are commonly used for such lenses include hydrogels, silicones and acrylic polymers.
Hydrogels have a relatively low refractive index which makes them less desirable materials because of the thicker lens optic that is necessary to achieve a given refractive power. Silicones have a higher refractive index than hydrogels, but tend to unfold explosively after being placed in the eye in a folded position. Explosive unfolding can potentially damage the corneal endothelium and/or rupture the natural lens capsule. Acrylic polymers are currently the material of choice since they typically have a high refractive index and unfold more slowly or controllably than silicone materials.
An important feature in the design of modern IOL's made of high refractive index material is that lenses can be made thinner which allows for a specific design of the lens being rolled in smaller dimensions. This consequently necessitates a smaller incision size in lens cataract surgery with the advantage of reduced risks for complications like astigmatism or complications related to incision healing.
A further requirement for IOL material is that rolling the lens does not induce tears or wrinkles so that after release of the lens from the cartridge nozzle the lens unfolds in a controlled way to its prerolled dimensions without its optical quality being compromised. The material must also be stiff enough such that thin high refractive index lenses do not deform when residing in the eye. After all, lenses must remain flat to retain their optical properties.
U.S. Pat. No. 5,290,892 discloses high refractive index, acrylic copolymers suitable for use as an IOL material. These acrylic copolymers comprise acrylate monomers, methacrylate monomers and a cross-linking monomer. Preferably, the copolymer has a glass transition temperature of about 20° to 25° C., an elongation of at least 150%. The refractive index at 20° C. of the copolymers disclosed in the Examples are not higher than 1.5584 (Example 10).
U.S. Pat. No. 5,331,073 discloses acrylic copolymers suitable for use as IOL materials. These copolymers comprise two acrylic monomers which are defined by the properties of their respective homopolymers. The first monomer is defined as one in which its homopolymer has a refractive index of at least about 1.50. The second monomer is defined as one in which its homopolymer has a glass transition temperature less than about 22° C. These IOL materials also contain a cross-linking monomer. Example 3 discloses a copolymer having an elongation of 143% and a refractive index of 1.55.
U.S. Pat. No. 5,693,095 and EP A 485.197 disclose copolymers that are suitable as IOL materials. These copolymers comprise a hydrophilic monomer and an aryl acrylic hydrophobic monomer having the general formula:
wherein X is hydrogen or methyl, m is an integer of 0-6, Y is a direct bond, O, S or NR(R may be alkyl) and Ar is an optionally substituted aromatic group. The copolymers have preferably a refractive index of at least 1.50, a glass transition temperature of −20° to 25° C. and an elongation of at least 150%. The examples show a highest refractive index of 1.544.
U.S. Pat. No. 6,140,438 discloses an IOL material comprising a copolymer of a hydrophilic monomer, an alkyl(meth)acrylate wherein the alkyl group has 1-20 carbon atoms, and an aromatic ring containing (meth)acrylate monomer of the formula:
wherein R1 is hydrogen or methyl, n is an integer of 0-5, X is a direct bond or oxygen, and R2 is an optionally substituted aromatic group. The copolymer has a water absorptivity of 1.5 to 4.5 wt. % and has an improved transparency.
The copolymers disclosed above all comprise at least two acrylic monomers and a cross-linking monomer. However, the required use of two acrylic monomers to adjust the glass transition temperature to around ambient temperature or below (as otherwise the lenses cannot be folded without damaging the lens) has the disadvantage that the refractive index is also lowered.
U.S. Pat. No. 6,653,422 discloses acrylic monomers of the formula:
wherein it is preferred that A is hydrogen or methyl, B is —(CH2)m— wherein m is an integer of 2-5, Y is a direct bond or oxygen, C is —(CH2)w— wherein w is an integer of 0 or 1 and Ar is phenyl. The IOL material is made from these monomers only and a cross-linking monomer. The refractive index is at least 1.50, de glass transition temperature is preferably below 25° C. and the elongation is at least 150%. According to the examples, the copolymer made of 3-benzoyloxypropyl methacrylate (B=3, Y=O, w=1, Ar=phenyl) and polyethylene glycol 1000 dimethyacrylate has the highest refractive index (dry state) which is 1.543 (Example 11).
US 2005/0049376 discloses curable (meth)acrylate compositions suitable for optical articles and in particular for light management films. Apart from a high refractive index, these compositions when cured have desirably a high glass transition temperature for shape retention during storage and use of the light management films. Tables 7 and 8 disclose glass transition temperatures of 41°-62° C. The refractive index of a composition made of 1,3-bis(thiophenyl)propane-2-yl acrylate and the diacrylate of tetrabromo bisphenol A diepoxide has a refractive index as high as 1.6016 (Example 14). Although generally having a high refractive index, the compositions are obviously unsuitable for IOL's because of their high glass transition temperatures. U.S. Pat. No. 6,833,391 also discloses high refractive index monomers.
It is therefore an object of the invention to provide acrylate compositions having a high refractive index as well as a low glass transition temperature, in particular a glass transition temperature of lower than 25° C., so that they are suitable for the manufacture of IOL's, in particular flexible IOL's.